Code receiver responsive to plural tones in sequence



2 Sheets-Sheet 1 GEORGE M. HANUS 8) WW {1 M4,

G. M. HAN US m2; mwzommmm m 4m 2 25 6 Nov. 28, 1967 CODE RECEIVERRESPONSIVE TO PLURAL TONES IN SEQUENCE Filed Jan. 14, 1965 WM 20%QwFEEmZAEk N QE Nov. 28, 1967 HANUS 3,355,709

CODE RECEIVER RESPONSIVE TO FLURAL TONES IN SEQUENCE Filed Jan. 14, 19652 Sheets-Sheet 2 TO DISCRIMINATOR FIG. 3

TONE OS OUTPU 31: meg-505%: 1 82 18 2 lnvenror y GEORGE M. HANUS WW a MUnited States Patent Office 3,355,?iifi Patented l lov. 28, lfidi35,355,799 CGBE RECEHVER REfiPONSlVE 'llfi PLURAL TONES EN SEQUENCEGeorge M. Hanus, Norridge, 11L, assignor to Motorola, Inc., FranklinParis, Ill, a corporation of lllinois Filed Jan. 14, 1965, Ser. No.425,593 14- Clairns. (Cl. 340-164) This invention relates generally totone decoder systems, and more particularly to a decoder systemresponsive to tones applied in a predetermined sequence and whichprevents false operation.

In selective signalling equipment, it is desired in many cases toprovide an alert signal of some type in response to reception of aplurality of tone signals. It has become quite common to use frequencyselective reed devices in tone decoders, because such devices provide avery sharp response to select signals of one frequency from signals ofclosely adjacent frequencies. Miniature reed devices have been providedfor small portable units, such as paging units, wherein selective alarmsare provided. However, such portable units may be dropped or otherwisesubjected to shock which can cause vibratory movement of the reeds toprovide false alarm signals. Another problem is that the received signalmay include simultaneously a large number of frequencies including thefrequencies to which the tone selective devices respond to cause falseoperation. Although the tone signals used may generally be in the audiofrequency range, the systems described will operate with tone signals ofhigher frecpienciesv It is an object of the present invention to providea tone decoder system for responding to a plurality of tone signals in asequence, and which will not respond to simultaneous application of thetone signals.

Another object of the invention is to provide a tone decoder systemincluding resonant reed devices for providing tone selection, whereinsimultaneous vibration of the reed devices will not produce an alarmsignal.

A further object of the invention is to provide a transistorized tonedecoder circuit having resonant reed selective units, wherein thesection responsive to the second tone signal is disabled except for ashort period after reception and termination of the first tone signal.

A feature of the invention is the provision of a decoder circuitresponsive to a plurality of tones of different frequencies applied insequence, including a selective device for each tune, a detector forresponding to each preselected tone with the detector for one toneacting to enable the detector for the next succeeding tone for a periodof time, and a disabling circuit connected from the detector for the onetone to the detector for the succeeding tone to disable the same untilafter termination of the one tone. The circuit can respond to two tonesin sequence, or to a. greater number of tones applied in sequences.

Another feature of the invention is the provision of a tone decodersystem including a plurality of resonant reed devices each coupled to atransistor detecting circuit, with the detecting circuit for the firsttone applying a first potential to the detecting circuit of the secondtone to enable the same when the first tone is received, and thedetecting circuit for the first tone applying a second potential to thedetecting circuit for the second tone for disabling the same until aftertermination of the first tone. The detecting circuit for the first toneincludes two portions having difierent time constants coupled to thedetecting circuit for the second tone so that the second disablingpotential is removed from the second detecting circuit while thisdetecting circuit is enabled by the first potential, so that thedetecting circuit can respond to the second tone when it is receivedafter termination of the first tone.

A further feature of the invention is the provision of a decoder systemwhich is responsive to either of two different pairs of tone signalsapplied in sequence, and which acts to disable the detector for thesecond tone of each pair during reception of the first tone of each pairand provides response to either pair only when the tones thereof aretransmitted in sequence.

The invention is illustrated in the drawing wherein:

FIG. 1 is a schematic diagram of the decoder circuit of the inventioncoupled to a receiver, with the stages of the receiver being shown inblock. diagram;

FIG. 2 is a chart illustrating the operation of the decoder circuit ofFIG. 1;

FIG. 3 is a circuit diagram of a decoder system responsive to threetones in sequence; and

FIG. 4 is a circuit diagram of a decoder system responding to either oftwo different tones applied in sequence.

In practicing the invention there is provided a transistorized decodercircuit which may be used in a radio receiver to provide an alert uponthe reception of a plurality of tones in sequence. The decoder circuitis coupled to the output of the modulation detector of the receiver, andapplies the signals therefrom simultaneously to a plurality of resonantselective devices. The selective devices may include resonant reeds toprovide sharp selectivity at a particular frequency. Each. selectivedevice is coupled to an amplifier and a tone detector which provides anoutput voltage when the tone is received. The amplifier for the secondtone is normally biased off and voltage is applied thereto from theoutput of the first detector to render it conducting. A clamping circuitis connected to the output of the tone amplifier for the second tone todisable the same, and this is rendered operative by a voltage from thedetector for the first tone. The clamping action is removed, however,after the first tone ceases, whereas the voltage applied to theamplifier continues so that the second tone is applied to the detectortherefor when it appears following the termination of the first tone. Anumber of detectors must be provided corresponding to the number oftones in the sequence, and each detector can enable the following one sothat each detector will respond only to tones applied in the propersequence. The detector for the last tone can actuare an alarm, or enablean audio amplifier so that the receiver audio output is translated. Thisaction may be provided through operation of an oscillator renderedconducting when the last tone is received in its proper order.

A decoder system may be provided which is responsive to any one of aplurality of different tone pair combinations, with a single clampingtransistor used to prevent false operation. In such case the clampingtransistor is actuated by either of the detectors for'the first tones ofthe pairs to disable the amplifier for the second tones of the pairs.

Referring now to the drawing, the decoder of the invention isillustrated in FIG. 1 for use with a frequency modulation receiver.Signals from antenna 16 are applied to radio frequency amplifier ll,wherein the level of the signals is increased. The amplified signals areapplied to converter 12, which may include one or more stages offrequency conversion, and may also include separate oscil lators forproviding heterodyning signals. The reduced frequency signals fromconverter 12 are applied to intermediate frequency amplifier 13, andfrom the amplifier to limiter 14. The limited signals are applied todiscriminator 15 wherein the modulation signals are derived from thefrequency modulated wave. The modulation signals are applied throughaudio amplifier 16 and audio output circuit 17 to a loudspeaker iii. Theaudio amplifier 16 may be normally biased oil, and rendered conductingwhen a a control signal is applied thereto. The portion of the receiverwhich has been described may be of standard wellknown construction.

The modulation signals from the discriminator T are applied throughcapacitor 26 to the base of transistor 21, which together with diode 22act to amplify and limit the signals. The output signals are applied toinput windings of resonant reed devices 24 and 26. The devices 24 and 26include a resonant magnetic reed with input and output windings coupledthereto. When the frequency to which the reeds are resonant is appliedto the input windings, the reeds will vibrate to produce signals in theoutput windings thereof. When a tone signal is received which is of thefrequency to which the device 24 responds, tone signals will be appliedfrom the output winding thereof to the transistor 23 which is connectedas a forward biased transistor amplifier. The amplified tone output isapplied through capacitor 29 to transistor 36 which functions as a tonedetector. When a signal of sufficient level is applied to the transistor30, this transistor conducts to charge capacitor 31 from the voltage onbattery 32. The voltage across capacitor 31 is applied to the voltagedivider including resistors 33 and 34, the common terminal of which isconnected to the base of transistor 35. When capacitor 31 charges to apredetermined value the voltage applied to transistor 35 causes thistransistor to conduct and provide the output of the tone detector.Feedback is applied from the collector electrode of transistor 35 to thebase electrode of transistor 36, through resistor 32.

The reed of device 26 will be selected to respond to the second tone ina sequence, and whenever this tone is present it will be applied fromthe output of resonant device 26 to the base of transistor 36.Transistor 36 is biased off by the potential applied from battery 32through resistor 37 and the output winding of device 26 to the baseelectrode of transistor 36. However, when transistor 35 conducts, thisacts to ground resistor 38 so that the bias voltage applied to the baseof transistor is reduced and this transistor is rendered conducting. Theoutput of tone amplifier transistor 36 is applied through capacitor 39to transistor 40 to render the same conducting to charge capacitor 41.Voltage across capacitor 41 is applied to the voltage divided includingresistors 43 and 44, the common terminal of which is connected to thebase of transistor 45. Feedback is provided from the collector electrodeof transistor 45 to the base electrode of transistor 40 through resistor42. It will be obvious that the circuits for amplifying and detectingthe two tones are quite similar.

Transistor 48 is connected to clamp the output of tone amplifier 36,when the transistor 48 is conducting. The voltage across capacitor 31 isapplied through resistor 49 and across resistor 56 to the base electrodeof transistor 48 to render it conducting. Resistor 49 has a greatervalue than resistor 33, and resistors 34 and 50 have the same value, sothat a larger portion of the voltage of capacitor 51 is applied totransistor 35 to hold the same conducting for a longer period thantransistor 48 is held conducting.

Accordingly, transistor 36 is rendered conducting as soon as the firsttone is detected and transistor 35 is rendered conducting. However, thesecond tone amplified by transistor 36 is shorted out by transistor 48until after the first tone is terminated. Therefore, the output of thesecond tone detector (transistor 45) appears only after the first tonehas been received to render transistor 36 conducting, and after thefirst tone has terminated so that transistor 48 is cut off to remove theclamp. Diode 46 connected from the collector electrode of transistor 45to resistor 38, grounds this resistor as long as the second tone isreceived to hold transistor 36 conducting for the duration of the secondtone.

The operation of the decoder system which has been described isillustrated in FIG, 2. Chart 1) illustrates the tones which may betransmitted, with tone A of a first frequency having a duration of aboutone second.

The interval between tones A and B may be about 400 milliseconds, andtone B may have a duration of at least one second or longer. Chart (2)of FIG. 2 shows the output of the channel A detector, which is theoutput of transistor 35 in FIG. 1. The time constant provided bycapacitor 31 and resistors 33 and 34 will hold the transistor 35conducting for about one second after tone A is terminated. Chart (3)shows the period of time that channel B, which detects tone B, isresponsive to the tone signal. This period is initiated by cut ofi oftransistor 43, and terminated by termination of conduction of transistor36. As previously stated, the voltage across capacitor 31 applied totransistor 48 is less than that applied to transistor 35, so thattransistor 48 remains conducting for a shorter period than transistor36. Transistor 48 may be conducting for about 600 milliseconds aftertone A is terminated. This leaves the remainder of the one secondperiod, or a period of about 400 milliseconds, during which channel B isresponsive. If tone B is applied to the second channel during thisperiod, this tone will be applied from amplifier 36 through capacitor 39to transistor 40 to render the same conducting to charge capacitor 41.Feedback through diode 46 holds amplifier 36 conductive for the durationof the second tone. The time constant of capacitor 41 and resistors 43and 44 controls the period of conduction of transistor 45 at thetermination of tone B. As stated above, the B channel is responsive fora period of about 400 milliseconds, and the tone may be continuedthereafter for a period of one second or longer, so that transistor 45may be conducting for a period of more than one second.

The transistor 45 when conducting causes operation of an oscillator 51.Resistors 52 and 53 are connected from the collector of transistor 45 tothe battery 32. When transistor 45 conducts, resistor 52 is groundedthereby so that resistors 52 and 53 form a voltage divider connected tothe battery 32. This applies a bias to the base of transistor 55 causingthis transistor to conduct. Inductor 56 and capacitors 57, 58 and 59cooperate with transistor 55 to form a tone oscillator, so thatoscillations are produced when transistor 55 conducts. The output ofoscillator 51 is applied to audio amplifier 16 to render the audioamplifier conductive when the tone signals to which resonant reeddevices 24 and 26 respond are received in their proper sequence.

FIG. 3 shows a decoder system for use with three tones applied insequence. The circuit is generally similar to that of the decoder inFIG. 2 and corresponding parts have been given the same numbers. A thirdresonant reed frequency selective device 62 has its input windingconnected in series with the input windings of frequency selectivedevices 24 and 26. This applies signals of a particular frequency to thebase electrode of transistor 63, which is normally biased to anon-conducting condition. When transistor 45 of the detector for thesecond tone conducts, resistor 64 is grounded to reduce the bias ontransistor 63 to render it conducting. The output of transistor 63 isclamped to ground by transistor 65 which performs the same function astransistor 48 in the circuit for detecting the second tone. This iscontrolled by the potential across capacitor 41 which is applied acrossresistors 67 and 68. This holds the circuit for the third tone clampedto ground until the second tone is terminated and the voltage acrosscapacitor 41 falls to a value such that transistor 65 is cut olf.

The tone output for the third tone is applied through capacitor 69 tothe base of transistor 70. Transistor 70 when conducting chargescapacitor 7-1 to render transistor 72 conducting. Transistor 72 groundsresistor 73 of the voltage divider 73, 74 to render the tone oscillator51 operative. Transistor 72 acts through diode 75 to ground resistor 64to hold transistor 63 conducting as long as the third tone is received.The tone oscillator may be used to render an audio amplifier conductingin a system as shown in FIG. 1, or may be used to provide an alarm J orany other control. The operation of the tone oscillator is the same asin the system of FIG. 1.

FIG. 4 shows a detector system which will respond to either of two pairsof tones applied in sequence. The drive amplifier 80 applies signals toresonant reed devices 81, d2, 83 and 84. Reed device 81 applies thefirst tone to amplifier 85 which in turn applies amplified signals todetector transistors 86 and 87. Resonant reed device 83 responds to thesecond tone of the first group and applies the tone to the amplifierincluding transistor 88, which is normally cut oflt. When transistor 86conducts in response to the first tone, capacitor 89 charges to apply apotential to actuate transistor 37. When transistor 87 conducts,transistor 88 is rendered conductive to amplify the second tone.Capacitor 89 also applies potential through resistor 90 to clampingtransistor 91 to short the output of transistor 88. When the first toneceases, transistor 91 is cut off so that the tone output of transistor83 is applied to detector transistors 92 and 93. This system operates inthe manner described in connection with FIG. 1 so that when the twotones are received in sequence, transistor 93 is rendered conducting tocause operation of tone oscillator $4. Transistor 93 also acts throughdiode '79 to apply a bias to transistor 88 to hold the same operative aslong as the second tone is received.

The system of FIG. 4 is also responsive to a second pair of tones, whichhave the frequencies selected by resonant reed devices 82 and 84.Devices 32 applies the signals selected thereby to transistor 95 whichamplifies the signal and applies the same to detector transistors 96 and97. These transistors operate in the manner previously described. Reeddevice 84 applies the selected tone to transistor 98 which is normallybiased off. When transistor 97 conducts, a voltage is applied to rendertransistor 98 conducting. However, the voltage developed acrosscapacitor 99 by conduction of transistor 96 is applied through resistorlitltl to transistor 91. This clamps the output of transistor 98 as wellas the output of transistor 83. When the first tone ceases andtransistor 91 is cut off to remove the clamp, the output of transistor98 is applied to detector transistors 92 and 93 to cause operation ofthe tone oscillator 94 in the manner previously described. The signalclamp transistor 91 prevents falsing by simultaneous operation of thetwo tones of either tone combination. Transistor 93 operates throughdiode 101 to hold transistor 98 operative as long as .the second tone isreceived.

Simultaneous operation of tones to which any two of the selectivedevices 81, 82, 83 and 84- respond will not cause a detector output. Thedetector output will be produced only when the tone selected by device81 is followed by the tone selected by device 83, or in response to thetone selected by device 82 followed by the tone selected by device 84.Inasmuch as both pairs of tones operate to provide the same control, thetone outputs of transistors 83 and 98 can be applied to a singledetector circuit and for this reason a single clamp transistor iseffective for both tone combinations.

In the circuit of FIG. 4 the battery 32 of FIGS. 1 and 3 has beenreplaced by a regulated power supply. The terminal 102 is connected to aminus potential which is applied through resistor 104 to the Zener diode1&5 in parallel with capacitor 106. The voltage across resistor 1% isapplied between the base and collector for transistor 16% to control theconduction thereof, so that the source volage is dropped by resistor 109and the resistance between the emitter and collector electrodes oftransistor 108 to provide a regulated voltage across capacitor 116.

The system of the invention has been found to be highly desirable fordecoder systems used in portable equipment. Since the portable equipmentis subjected to shock, the resonant reed devices may be mechanicallyexcited by the shock to provide signals which produce an alarm. However,in such case the devices would be simultaneously excited and this wouldnot cause operation of the decoder 6 system described. This is becausethe circuit responding to signals from the second resonant device cannotoper ate until the circuit coupled to the first resonant devicc removesthe clamp therefrom. Since the clamp is not re moved until after thefirst resonant device ceases to apply a signal to the first detectorcircuit, the second detector circuit cannot respond unless the secondresonant device continues to apply a signal after the first device hasstopped applying a signal. The circuit of the invention therefore,prevents false operation both in response tc simultaneous application oftwo tones to the system which may be present in an electrical signalapplied, and also in response to a mechanical excitation of the reeddevices.

I claim:

It. A decoder circuit for responding to first and second tone signals ofdifferent frequencies applied in sequence including in combination,first and second tone frequency selecting and detecting circuits, meansfor applying tone signals to said circuits, said first tone circuitproviding first and second output signals in response to a first tonesignal selected thereby, said first and second output signals continuingafter said first tone signal ceases with said first output signalcontinuing for a time period after said second output signal terminates,said second tone selecting and detecting circuit providing an outputsignal in response to a second tone signal selected thereby, said secondcircuit being coupled to said first circuit and being enabled by saidfirst output signal and disabled by said second output signal, wherebysaid second tone circuit produces an output signal only in response tosaid second tone signal applied after said first tone signal and in thetime period during which said first output signal continues aftertermination of said second output signal.

2. A decoder circuit for responding to first and second tone signals ofdifferent frequencies applied in sequence including in combination,first and second tone frequency selecting means, means for applying tonesignals to said selecting means, first tone detecting means connected tosaid selecting means and providing first and second output signals inresponse to a first tone signal selected by said first selecting meanswith said first output signal continuing for a time period after saidsecond output signal and said first tone signal terminate, second tonedetecting means connected to said second selecting means for providingan output signal in response to a second tone signal selected by saidsecond selecting means, said second tone detecting means including firstand second portions coupled to said first detecting means, with saidfirst portion being enabled by said first output signal and said secondportion being disabled by said second output signal, whereby said secondtone detecting means produces an output signal only in response to saidsecond tone signal applied after said first tone signal and in the timeperiod during which said first output signal continues after terminationof said second output signal.

3. A decoder circuit for responding to first and second tone signals ofdifferent frequencies applied in sequence including in combination,first and second tone frequency selecting devices, means for applyingtone signals to said selecting devices, first tone detecting meansconnected to said first selecting device and including means providing avoltage in response to a first tone signal selected by said firstselecting device, second tone detecting means connected to said secondselecting device for providing an output signal in response to a secondtone signal selected by said second selecting device, said second tonedetecting means including amplifier means normally biased to benon-conducting, first circuit means connecting said voltage providingmeans to said amplifier means to render the same conducting in responseto said first tone signal, clamping means connected to said amplifiermeans to disable the output thereof, second circuit means connectingsaid voltage providing means to said clamping means for rendering thesame operative, said first and second circuit means having timeconstants such that said amplifier means is held conducting aftertermniation of said first one signal for a longer time period than saidclamping neans is held operative, whereby said second tone detect ngmeans produces an output signal only in response to ;aid second tonesignal applied after termination of said irst tone signal and in thetime period during which said tmplifier means is held conducting aftersaid clamping neans is no longer held operative.

4. A decoder circuit for responding to first and second one signals ofdifferent frequencies applied in sequence ncluding in combination, firstand second tone frequency ;electing devices, means for applying tonesignals to said selecting device's, first tone detecting means connectedto ;aid first selecting device and including capacitor means acrosswhich a predetermined voltage is developed in response to a first tonesignal selected by said first selecting device, second tone detectingmeans connected to said second selecting device for providing an outputsignal in response to a second tone signal selected by said secondselecting device, said second tone detecting means including amplifiermeans normally biased to be non-conducting, first circuit meansconnecting said capacitor means to said amplifier means to render thesame conducting in response to said first tone signal, clamping meansconnected to said amplifier means to disable the output thereof, secondcircuit means connecting said capacitor means to said clamping means forrendering the same operative, said first and second circuit means havingtime constants such that said amplifier means is held conducting aftertermination of said first tone signal for a longer time period than saidclamp means is held operative, whereby said second tone detecting meansproduces an output signal only in response to said second tone signalapplied after termination of said first tone signal and in the timeperiod during which said amplifier means is held conducting after saidclamping means is no longer held operative.

5. A decoder circuit for responding to first and second tone signals ofdifferent frequencies applied in sequence including in combination,first and second tone frequency selecting means including vibratory reedelements responsive respectively to said frequencies of said first andsecond tone signals, means for applying tone signals to said selectingmeans, first tone detecting means connected to said first selectingmeans and providing first and second output signals in response to thefirst tone signal selected by said first selecting means, with saidoutput signals continuing after termination of said first tone signaland said first output signal continuing for a time period after saidsecond output signal terminates, second tone detecting means connectedto said second selecting means for providing an output signal inresponse to the second tone signal selected by said second selectingmeans, said second tone detecting means including a selectively disabledportion coupled to said first detecting means which is enabled by saidfirst output signal and disabled by said second output signal, wherebysaid second tone detecting means produces an output signal only inresponse to said second tone signal applied after termination of saidfirst tone signal and in the time period during which said first outputsignal continues after termination of said second output signal.

6. A decoder system for responding to first and second tone signals ofdifierent frequencies applied in sequence including in combination,first and second tone frequency selecting devices including vibratoryreed elements responsive respectively to said frequencies of said firstand second tone signals, means for applying tone signals to saidselecting devices, first tone detecting means connected to said firstselecting device and including means providing a voltage in response tosaid first tone signal, second tone detecting means connected to saidsecond selecting device for providing an output signal in response tosaid second tone signal, said second tone detecting means includingamplifier means normally biased to be non-conducting, first circuitmeans connecting said voltage providing means to said amplifier means torender the same conducting in response to said first tone signal,clamping means connected to said amplifier means to di able the outputthereof, second circuit means connecting said voltage providing means tosaid clamping means for rendering the same operative, said first andsecond means having time constants such that said amplifier means isheld conducting after termination of said first tone signal for a longertime period than said clamping means is held operative, whereby saidsecond tone detecting means produces an output signal only in responseto said second tone signal applied after termination of said first tonesignal and in the time period during which said amplifier means is heldconducting after said clamping means is no longer held operative.

7. A decoder system for use with a radio receiver having a detector andan audio amplifier selectively rendered operative by a control signal,said decoder system responding to first and second tone signals ofdifferent frequencies applied in sequence and including in combination,first and second tone frequency selecting devices including vibratoryreed elements responsive respectively to said frequencies of said firstand second tone signals, means for applying tone signals from thedetector of the receiver to said selecting devices, first tone detectingmeans connected to said first selecting device and including meansproviding a voltage in response to said first tone signal and outputmeans, second tone detecting means connected to said second selectingdevice for providing an output signal in response to said second tonesignal, said second tone detecting means including transistor amplifiermeans normally biased to be non-conducting, first circuit meansconnecting said output means to said amplifier means to render the sameconducting in response to said first tone signal, transistor switchmeans connected to the output of said amplifier means to short suchoutput when said switch means conducts, second circuit means connectingsaid voltage providing means to said transistor switch means forrendering the same conductive, said first and second means beingconstructed to hold said amplifier means conducting after termination ofsaid first tone signal for a longer time period than said switch meansis held conductive, whereby said second tone detecting means produces anoutput signal only in response to said second tone signal applied aftertermination of said first tone signal and in the time period duringwhich said amplifier means is held conducting after said switch means isno longer held conductive, and control means coupled to said second tonedetecting means and responsive to said output signal thereof to apply acontrol signal to the audio amplifier of the radio receiver to renderthe same operative.

8. A decoder system for responding to a plurality of tone signals ofdifierent frequencies applied in sequence including in combination, aplurality of tone frequency selecting devices each including a vibratoryreed element responsive to one of said tone signals, means for applyingtone signals to said selecting devices, a plurality of detecting meansconnected respectively to said selecting devices, said detecting meansconnected to said selecting devices responsive to all the tone signalsin the sequence except the last tone providing first and second outputsignals in response to the tone signal applied thereto, with said outputsignals continuing after the termination of the tone signal and saidfirst output signal continuing for a time period after said secondoutput signal terminates, said tone detecting means connected to saidselecting devices responsive to all of the tone signals in the sequenceexcept the first tone including a selectively disabled portion, saidselectively disabled portion of each detecting means being coupled tosaid tone detecting means for the preceding tone and being enabled bysaid first output signal therefrom and disabled by said second outputsignal therefrom, whereby said tone detecting means for all the tonesexcept the first tone produce an output signal only in response to saidtone signal applied thereto after termination of the preceding tonesignal and in the time period during which said first output signal fromsaid tone detecting means for the preceding tone continues aftertermination of said second output signal therefrom.

9. A decoder system for responding to a plurality of tone signals ofdifferent frequencies applied in sequence including in combination, aplurality of tone frequency selecting devices each responsive to one ofsaid tone signals, means for applying tone signals to said selectingdevices, a plurality of detecting means connected respectively to saidselecting devices, said detecting means connected to said selectingdevice responsive to all the tone signals in the sequence except thelast tone signal providing first and second output signals in responseto the tone signal applied thereto, with said output signals continuingafter the termination of the tone signal and said first output signalcontinuing for a time period after said second output signal terminates,said tone detecting means connected to said selecting devices responsiveto all of the tone signals in the sequence except the first toneincluding a selectively disabled portion, said selectively disabledportion of each detecting means being coupled to said tone detectingmeans for the preceding tone and being enabled by said first output sinal therefrom and disabled by said second output signal therefrom,whereby said tone detecting means for all the tones except the firsttone produce an output signal only in response to said tone signalapplied thereto after termination of the preceding tone signal and inthe time period during which said first output signal from said tonedetecting means for the preceding tone continues after termination ofsaid second output signal therefrom.

10. A decoder system for responding to a plurality of tone signals ofdifferent frequencies applied in sequence including in combination, aplurality of tone frequency selecting devices each responsive to one ofsaid tone signals, means for applying tone signals to said selecting devices, a plurality of detecting means connected respectively to saidselecting devices, said detecting means connected to said selectingdevices responsive to all of the tone sig nals in the sequence exceptthe last tone signal providing a control voltage and an output signal inresponse to the tone signal applied thereto, with said control voltageand said output signal continuing after the termination of the tonesignal and said output signal continuing for a time period after saidcontrol voltage terminates, said detecting means connected to saidselecting devices responsive to all of the tone signals in the sequenceexcept the first tone signal including amplifier means normally biasedto be non-conducting, first circuit means applying said output signalfrom the preceding detector means to said amplifier means to render thesame conducting, clamping means connected to said output of saidamplifier means and operative to disable said amplifier means, andsecond circuit means applying said control voltage from the precedingdetector means to said clamping means for rendering the same operative,said first and second circuit means being constructed to hold saidamplifier means of said detecting means for one tone signal conductingafter termination of the preceding tone signal in the sequence for alonger time period than said clamping means is held operative, wherebysaid tone detecting means for all tone signals except the first producesan output signal only in response to said tone signal applied theretoafter termination of the preceding tone signal and in the time periodduring which said amplifier means is held conducting and after saidclamping means has been operative.

11. A decoder system for responding to a plurality of tone signals ofdifierent frequencies applied in sequence including in combination, aplurality of tone frequency selecting devices each including a vibratoryreed element responsive to one of said tone signals, means for applyingtone signals to said selecting devices, a plurality of detecting meansconnected respectively to said selecting devices, said detecting meansconnected to said selecting devices responsive to all of the tonesignals in the sequence except the last tone signal providing a controlvolt-age and an output signal in response to the tone signal appliedthereto, with said control voltage and said output signal continuingafter the termination of the tone signal and said output signalcontinuing for a time period after said control voltage terminates, saiddetecting means connected to said selecting devices responsive to all ofthe tone signals in the sequence except the first tone signal includingtransistor amplifier means normally biased to be non-conducting, firstcircuit means applying said output signal from the preceding detectormeans to said amplifier means to render the same conducting, transistorswitch means connected to said output of said amplifier means to shortsuch output when said switch means conducts, and second circuit meansapplying said control voltage from the preceding detector means to saidtransistor switch means for rendering the same conductive, said firstand second circuit means being constructed to hold said amplifier meansof said detecting means for one tone signal conducting after terminationof the preceding tone signal in the sequence for a longer time periodthan said switch means thereof is held conductive, whereby said tonedetecting means for all tone signals except the first produces an outputsignal only in response to said. tone signal applied thereto aftertermination of the preceding tone signal and in the time period duringwhich said amplifier means is held conducting and after said switchmeans has been conductive.

12. A decoder system for responding to either of two pairs of tonesignals of diflerent frequencies wherein the tone signals of each pairare applied in sequence, said system including in combinaton, first,second, third and fourth tone frequency selecting devices, with saidfirst and second devices selecting the first pair of tones and the thirdand fourth devices selecting the second pair of tones, means forapplying tone signals to said selecting devices, first tone detectingmeans connected to said first selecting device and including firstimpedance means across which a first voltage is developed in response tothe tone signal selected by said first selecting device, first amplifiermeans connected to said second selecting device and being normallybiased to be non-conducting, first circuit means connecting said firstimpedance means to said first amplifier means to render the sameconducting in response to said first voltage, third tone detecting meansconnected to said third selecting device and including second impedancemeans across which a second volt-age is developed in response to thetone signal selected by said third selecting device, second amplifiermeans connected to said fourth tone selecting means and being normallybiased to be non-conducting, second circuit means connecting said secondimpedance means to said second amplifier means to render the sameconducting in response to said second voltage, clamping means connectedto said first and second amplifier means to disable the outputs thereof,third circuit means connected to said first and second impedance meansand to said clamping means for rendering the same operative in responseto one of said first and second voltages, said first, second and thirdcircuit means having time constants such that each of said amplifiermeans is held conducting for a longer time period than said clampingmeans is held operative, whereby each of said amplifier means producesan output only when a tone signal is applied thereto in the time periodduring which said amplifier is held conducting and after said clampingmeans has been operative, and third tone detecting means connected tosaid outputs of said first and second amplifier means for producing anoutput signal.

13. A decoder system for responding to either of two pairs of tonesignals of diiferent frequencies wherein the tone signals of each pairare applied in sequence, said system including in combination, first,second, third and fourth tone frequency selecting devices includingvibratory reed elements responsive respectively to said frequencies ofsaid tone signals of said first and second pairs, means for applyingtone signals to said selecting devices, first tone detecting meansconnected to said first selecting device and including first impedancemeans across which a voltage is developed in response to a first tonesignal selected by said first selecting device, first amplifier meansconnected to said second selecting device and being normally biased tobe non-conducting, first circuit means connecting said first impedancemeans to said first amplifier means to render the same conducting inresponse to said first tone signal to amplify a second tone signalselected by said second selecting device, third tone detecting meansconnected to said third selecting device and including second impedancemeans across which a voltage is developed in response to a third tonesignal selected by said third selecting device, second amplifier meansconnected to said fourth tone selecting means and being normally biasedto be non-conducting, second circuit means connecting said secondimpedance means to said second amplifier means to render the sameconducting in response to said third tone signal to amplify a fourthtone signal selected by said fourth selecting device, clamping meansconnected to said first and second amplifier means to disable theoutputs thereof, third circuit means connecting said first and secondimpedance means to said clamping means for rendering the same operative,said first, second and third circuit means having time constants suchthat each of said amplifier means is held conducting for a longer timeperiod than said clamping means is held operative, and third tonedetecting means connected to said outputs of said first and secondamplifier means for producing an output signal, said amplifier meansapplying a signal to said third tone detecting means only in response toone of said second and fourth tone signals applied after termination ofsaid first and third tone signals respectively in the time period duringwhich said amplifier means is held conducting after said clamping meansbecomes inoperative.

14. A decoder system for responding to either of two pairs of tonesignals of different frequencies wherein the tone signals of each pairare applied in sequence, said system including in combination, first,second, third and fourth tone frequency selecting devices each includinga vibratory reed element responsive to the frequency of one of said tonesignals, means for applying tone signals to said selecting devices,first tone detecting means connected to said first selecting device andincluding first capacitor means across which a voltage is developed inresponse to a first tone signal selected by said first selecting device,first transistor amplifier means connected to said second selectingdevice and being normally biased to be non-conducting, first circuitmeans connecting said first impedance means to said first amplifiermeans to render the same conducting in response to said first tonesignal to amplify a second tone signal selected by said second selectingdevice, third tone detecting means connected to said third selectingdevice and including second capacitor means across which a voltage isdeveloped in response to a third tone signal selected by said thirdselecting device, second transistor amplifier means connected to saidfourth tone selecting means and being normally biased to benon-conducting, second circuit means connecting said second impedancemeans to said second amplifier means to render the same conducting inresponse to said third tone signal to amplify a fourth tone signalselected by said fourth selecting device, transistor switch meansconnected to said first and second amplifier means to short the outputsthereof, third circuit means connecting said first and second capacitormeans to said transistor switch means for rendering the same conductive,said first and second circuit means having a time constant longer thansaid third circuit means so that each of said amplifier means is heldconducting for a longer time period than said switch means is heldconductive, and third tone detecting means connected to said outputs ofsaid first and second amplifier means for producing an output signal,said first amplifier means applying a signal to said third tonedetecting means only in response to said second tone signal appliedafter termination of said first tone signal and said second amplifiermeans applying a signal to said third tone detecting means only inresponse to said fourth tone signal applied after termination of saidthird tone signal in the time period during which such amplifier meansis held conducting after said transistor switch becomes non-conductive.

No references cited.

NEIL C. READ, Primary Examiner.

H. PITTS, Assistant Examiner.

1. A DECODER CIRCUIT FOR RESPONDING TO FIRST AND SECOND TONE SIGNALS OFDIFFERENT FREQUENCIES APPLIED IN SEQUENCE INCLUDING IN COMBINATION,FIRST AND SECOND TONE FREQUENCY SELECTING AND DETECTING CIRCUIT, MEANSFOR APPLYING TONE SIGNALS TO SAID CIRCUITS, SAID FIRST TONE CIRCUITPROVIDING FIRST AND SECOND OUTPUT SIGNALS IN RESPONSE TO A FIRST TONESIGNAL SELECTED THEREBY, SAID FIRST AND SECOND OUTPUT SIGNALS CONTINUINGAFTER SAID FRST TONE SIGNAL CEASES WITH SAID FIRST OUTPUT SIGNALCONTINUING FOR A TIME PERIOD AFTER SAID SECOND OUTPUT SIGNAL TERMINATES,SAID SECOND TONE SELECTING AND DETECTING CIRCUIT PROVIDING AN OUTPUTSIGNAL IN RESPONSE TO A SECOND TONE SIGNAL SELECTED THEREBY, SAID